1. Field of the Invention
The invention relates generally to methods for forming Extreme Ultraviolet (ELV) Lithography structures. More specifically, the invention relates to methods for forming high quality lithography glass structures with void spaces and more specifically, the invention relates to methods for forming low thermal expansion ELV Lithography glass reduced weight rigid support structures from ultra low expansion glass particles.
2. Background
Ultra low expansion glass, such as a type sold by Corning, Incorporated, Canton, N.Y. under the trade name ULE® glass is formed by a process known as flame hydrolysis. Chemical vapors are introduced into a gas-oxygen burner at approximately 1700° C. The combustion reaction forms sub-micron sized molten soot particles. The burners are generally aligned over a rotating table in a refractory furnace where the particles are collected and fused into a large, dense, solid boule of glass. Typical materials used to make such glass includes high-purity titanium-containing feedstock, such as titanium alkoxide, TiCl4 or titanium isopropoxide, and high purity silicon-containing feedstock, such as octamethylcyclotetrasiloxane or SiCl4. During the combustion process, titanium doped silica soot is formed. Much of the particle soot is deposited on the rotating table, but some of the soot is not deposited and becomes an exhausted waste product particle of the silica forming process which is collected in a baghouse. The soot typically has a very high purity and very small particle size.